Motorola ColdFire MCF5282 User Manual download pdf (Page 7)

Concantenation of Received Frames in 10BaseT Mode

MCF5282 Device Errata, Rev. 1.5

Freescale Semiconductor 7

Figure 1. Buffer Overrun Example

9.2 Workaround

There are three independent workarounds:

1. Only use 100BaseT.

2. Allocate extra lines for the receive data buffers. The actual allocated memory for each buffer

should be equal to the receive buffer size programmed in the FEC’s EMRBR register plus four

lines (16 byte-sized lines).

3. Program the data buffer size one line larger than the max packet size

(data buffer size = EMRBR + 0x40).

STATUS: Will be fixed

DATECODES AFFECTED: All

10 Concantenation of Received Frames in 10BaseT

Mode

10.1 Description

When the FEC is connected to a 10BaseT network, sometimes the FEC will combine the data from

multiple frames to generate a single frame. The data from the frames is received correctly, but the frame

boundary is not reported correctly. This causes the descriptor to report the length as the data length for all

of the concantenated frames added together. The incorrect data length might exceed the max frame length

programmed in the RCR[MAX_FL] field.

When TCP is used as a transport mechanism, this errata will manifest itself as lost packets and reduced

throughput. Data will still ultimately be received correctly, because TCP will request retransmission of bad

packets. However, UDP does not include any mechanism for packet retransmission, as it is a 'send and

forget' protocol. Consequently, while UDP should be able to identify a packet that is received incorrectly

buffer start + 0x5F0

buffer start + 0x5E0

buffer start + 0x600

buffer start + 0x610

buffer start + 0x620

buffer start + 0x630

End of data buffer

Valid frame data

Expected extra data

Unexpected data/

overflows the data buffer

1 2 3 4 5 6 7 8 9 10 11 12

No comments

Motorola ColdFire MCF5282 User Manual Page 7